1. Field of the Invention
The subject invention relates to the translation of mechanical forces, such as tension and compression, into corresponding electrical signals, and, more specifically, to beam design, diaphragm structure, transducer construction, strain gauge systems, chemical etching or milling methods, and various methods for making stress distribution plates, beams and diaphragms.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments subsequent in time or priority.
Various methods have been employed in the past to improve the performance of strain gauge/diaphragm type pressure transducers, particularly with respect to the location of the strain gauges bonded to the diaphragm to measure the tensile (expansion) and compressive (contraction) strain of the diaphragm when it is subjected to stress in the form of pressure exerted against the diaphragm. Unfortunately, many of such prior manufacturing techniques have become impractical due to the increasing cost of manufacture and the complicated steps that have been employed. Also, many prior devices suffer from inherent instability and a relatively low output of the strain gauges.
These problems are particularly acute in connection with low pressure/small diameter diaphragm type transducers which incorporate integrally bonded strain gauges on the diaphragms. The size of the gauges and their location on the diaphragm are of primary importance in connection with output/input efficiency, stability/time performance, and the effort to obtain linearity and to minimize hysteresis problems.
Ideally, the center of one or more strain gauges is placed to coincide with the center of the maximum amplitude of the tensile strain locations, and another set of gauges is attempted to be placed to overlie a corresponding center for maximum amplitude of compressive strains. In the past a primary problem has arisen with the maximum compression amplitude which is typically at the very outer edge of a conventional diaphragm. Those methods which have sought to distribute this maximum compressive strain location inwardly toward the center have invariably added excessively to the cost of the process and are therefore rather impractical as well as somewhat unreliable.
Some references of interest are mentioned below in the context of FIGS. 1 to 5 and other parts of the drawings. These references are of record in the parent applications and are herewith incorporated by reference herein.
Further references are also of record or on file in the parent applications and are herewith incorporated by reference herein. By way of example, these include U.S. Pat. No. 3,335,381 by M. Di Giovanni, and U.S. Pat. No. 3,341,794, by C. K. Stedman, utilizing a boss center section supported by an annular flexure region having strain gauges located thereon.
Such prior proposals provide only localized high-stress areas, but provide no significant mechanical amplification.
Also, the proposals just discussed are limited in terms of manufacture to conventional machining, being time-consuming and expensive and being restricted in terms of minimum attainable diaphragm thickness. Because the large central boss or mass places such transducers into the category of accelerometers they are generally useless for dynamic pressure measurements.
Further references of record or on file in the parent applications, including U.S. Pat. No. 4,050,049, by A. P. Youmans, U.S. Pat. No. 4,071,838, by B. Block, and U.S. Pat. No. 4,144,516, by H. E. Aine, are limited in terms of photolithographic and etching techniques on silicone wafers and other solid-state materials.
Reference may also be had to U.S. Pat. No. 3,049,685, by W. V. Wright, which shows a diffused silicon beam transducer lacking mechanical amplification.